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Interview Questions and Answers for 'Polaris' - 19 question(s) found - Order By Newest

Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )
 Q1. What are different ways of object creation in Java ?Core Java
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Ans. Using new operator - new xyzClass()

Using factory methods - xyzFactory.getInstance( )

Using newInstance( ) method - (Class.forName(xyzClass))emp.newInstance( )

By cloning an already available object - (xyzClass)obj1.clone( )

  Sample Code for object initialization using clone

  Sample Code for object initialization using getInstance

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   Like         Discuss         Correct / Improve     java   oops   object creation   new operator   class.forname   cloning   ebay     Asked in 9 Companies      expert


 Q2. Which of the following combination of keywords is illegal in Java ?

a. static and transient
b. transient and final
c. static and synchronized
d. abstract and final
Core Java
Anonymous
Ans. abstract and final

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   Like         Discuss         Correct / Improve     java   java keywords     Asked in 2 Companies      basic


Basic and Very Frequently asked.
  Q3. What is Polymorphism in Java ?Core Java2016-11-06 09:10:54

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

  Sample Code for overloading

  Sample Code for overriding

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   Like         Discuss         Correct / Improve     polymorphism  object oriented programming (oops)  oops concepts  oops concepts     Asked in 107 Companies      Basic        frequent

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  Q4. What is a String Pool ?Core Java
Anonymous
Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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   Like         Discuss         Correct / Improve     java   oops   string   string class   string pool   heap memory     Asked in 30 Companies      intermediate        frequent

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q5. Differences between abstract class and interface ?Core Java
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Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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   Like         Discuss         Correct / Improve     java   classes   abstract class   interfaces     Asked in 65 Companies      basic        frequent


 Q6. Difference between JVM, JRE and JDK ?Core Java2017-10-31 08:36:22

Ans. JDK(Java Development kit) = Development Kit comprising of JVM , library and development tools for developers

JRE (Java Run time Environment) - Comprise of JVM and set of libraries

JVM(Java Virtual Machine) = Interpreter which reads the .class file line by line.

When we install JDK, JRE also get installed so we can write,compile and excute our code. Used by developer. Without JDK we can only execute the program using JRE.

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   Like         Discuss         Correct / Improve     jvm  jre  jdk  jvm vs jre vs jdk     Asked in 4 Companies


Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies.
  Q7. Difference between Overloading and Overriding ?Core Java
Anonymous
Ans. Overloading - Similar Signature but different definition , like function overloading.

Overriding - Overriding the Definition of base class in the derived class.

  Sample Code for overloading

  Sample Code for overriding

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   Like         Discuss         Correct / Improve     java   oops   overloading   overriding   oops concepts   basic interview question     Asked in 82 Companies      basic        frequent

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 Q8. What is Generalization and Specialization in terms of casting ?Core Java
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Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.

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   Like         Discuss         Correct / Improve     java   data types   casting  type casting   up casting  type casting   downcasting  type casting   generalization   specialization     Asked in 2 Companies


 Q9. What does String intern() method do?Core Java
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Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

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   Like         Discuss         Correct / Improve     java   string class   string   intern method   garbage collection   advanced     Asked in 2 Companies      expert


Frequently asked in CTS ( Based on 2 feedback )
  Q10. What is the difference between comparable and comparator in java.util pkg?Core Java
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Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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   Like         Discuss         Correct / Improve     java   java.util   comparable   comparator   collections     Asked in 23 Companies      basic        frequent


 Q11. What is a Class ?Core Java
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Ans. A class is a blue print or Mold using which individual objects are created. A class can contain fields and methods to describe the behavior of an object.

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   Like         Discuss         Correct / Improve     java   oops   class   basic interview question     Asked in 1 Companies      basic        frequent


  Q12. What is the use of HashCode in objects ?Core Java
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Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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   Like         Discuss         Correct / Improve     java   string   hashcode   hash code   string comparison  hashtable     Asked in 17 Companies      basic        frequent


  Q13. Can we have null keys in TreeMap ?Core Java
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Ans. No, results in exception.

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   Like         Discuss         Correct / Improve     java   collections   treemap     Asked in 6 Companies      Basic        frequent


Frequently asked in face to face interviews.
  Q14. Write a program to print fibonacci series.Core Java

Ans. int count = 15;
int[] fibonacci = new int[count];
fibonacci[0] = 0;
fibonacci[1] = 1;
for(int x=2; x < count; x++){
fibonacci[x] = fibonacci[x-1] + fibonacci[x-2];
}

for(int x=0; x< count; x++){
System.out.print(fibonacci[x] + " ");
}

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   Like         Discuss         Correct / Improve     ebay   fibonacci series     Asked in 65 Companies      basic        frequent


 Q15. Why can't we declare a class abstract as well as final ?Core Java

Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together.

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   Like         Discuss         Correct / Improve     abstract   final   java keywords     Asked in 1 Companies


Frequently asked in high end product companies. Frequently asked in Deloitte.
  Q16. How is Hashmap internally implemented in Java ?Core Java2016-12-06 08:49:37

Ans. https://www.quora.com/How-is-Hashmap-in-Java-implemented-internally-What-are-the-pros-and-cons-to-use-it-What-are-the-complexities-it-provides-for-insert-delete-and-lookup/answer/Anshudeep-Bajpai?srid=iwnK

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   Like         Discuss         Correct / Improve     hashmap  collections  hashmap internal implementation     Asked in 18 Companies      expert        frequent


 Q17. When should we use Abstract classes ?Core Java2016-12-23 20:12:52

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as inheritance ( extending abstract class ). So they should be used in place of interfaces in case there is some code ( methods ) or object body ( member elements ) that can be reused with inheritance.

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   Like         Discuss         Correct / Improve     abstract classes     Asked in 1 Companies


 Q18. Will the following code compile ?

final HashMap hm = new HashMap();
hm.put("Ravi", 221);
Core Java2017-07-17 08:08:58

Ans. Yes, it will compile without error. final in this context means that the reference hm cannot be assigned to a new hash map but didn't restrict from changing the state of collection already held by hm.

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   Like         Discuss         Correct / Improve     final  final variable     Asked in 1 Companies


 Q19. What is abstraction ?2017-10-13 09:23:38

Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user.

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   Like         Discuss         Correct / Improve          Asked in 20 Companies




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